Twist-drill



(No Model.) 7

0. TYBHRG. TWIST DRILL.

No. 546,041. Patented Sept .10, 1895.

WITNESSES: I l/vm mfl 4% fig .Q/ Z9 012M v Arm/Mm,

OLUF TYBERG, or BROOKLYN, NEW YORK.

TWI lST-DRI LL.

SPECIFICATION forming part of Letters Patent No. 546,041, dated September 10, 1895..

- Applica i n fi October 2, 189 Serial No. 524,748. (No model.)

To ctZZ whom it may concern.-

Be it knownthat I, OLUF TYBERG, a subject of the King of Denmark, residingin Brooklyn, in the county of Kings and State of New York, have invented certain new and useful Improvements in Twist-Drills, of which the following is a specification, reference being had therein to the accompanying drawings.

In twist-drills as heretofore made, so far as I am aware, neither of the cuttingedges extends to the axial center of the drill, and usually the two cutting-edges are tangential to a small circle of which the axis is the center. The center portion, therefore, of such drills must remove the stock by a crushing or scraping action only, resulting in a retardation of the feed and development of considerable frictional heat.

The object of my invention is to produce a twist-d rill in which the true cut of the tool extends to its axis. To this end I so modify the cross-sectional shape as to produce two outting-edges, one of which is of the usual character, but extends inward to the axis of the drill. The modification of cross-section consists in having one of the grooves extend to the axis, while the opposite one is of such shape as to leave a sufficiently substantial connection on that side of the axis between the two sides of the drill. I am aware that in twist-drills in which neither of the grooves extends to the axis it has been proposed to grind a chamfer on the stock connecting the two sides of the drill and to thus attempt to extend the cutting-edge to or closer to the axis. Such an operation is, however, difficult, requires a sharp-edged grinding wheel or tool, and is unsatisfactory in results. I am also aware that it has been proposed to make a twist-drill in which one of the grooves is extended beyond the axis, thus removing the central portion of the drill entirely. In such case a core corresponding to this central portion would remain in the center of the hole unless the hole be drilled entirely through the stock. Such a drill would be difiicult to start, not having a center, and it would be practically impossible to grind it. In the accompanying drawings, Figure 1 is a side view of a drill embodying my invention; Fig. 2 an end view,and Fig. 3 a section, through any portion of the drill. Figs. 4, 5, and 6 are views, respectively, similar to Figs. 1 2, and 3, showing a somewhat modified form of my invention. Figs. 7 and 8 show sections of two other modifications embodying the sameinvention. Referring to Fig. 3, this section shows the drill to have two spirally-cut angular grooves,

one of which a O b has its apex in the center or axis of the drill throughout its entire 5.

length, while the other groove 0 np' d is shaped so as to leave sufficient stock around the other portion of the center to connect the two sides of the drill which carry the cuttinglips or cutting-edges. These lips a 0 and c o are shown in Figs. 1 and 2. When grinding the drill and relieving the stock behind the lips, it is possible to grind in such a manner as to procure two perfect cutting-edges, both running directly to the axis of the drill, by removing the stock in front of the cuttingedge 0 0, as indicated in Fig. 1 byline o n. This, however, is not absolutely necessary, as it is sufficient if only'one cutting-edge a 0 runs directly to the center, which the shape of the groove a 0 b will always insure.

Figs. 4.,- 5, and 6 show a drill formed in a similar manner, except the shapes of the grooves are somewhat modified, so as to obtain a lighter drill, and illustrate how the circular relief indicated by lines o b and a d used in some of the present drills may also be obtained in my drill.

Fig. 7 illustrates the accomplishment of my invention by two rectangular V-shaped grooves a 0 b and c n 01 Fig.8 shows how the cutting-edges a O and c n may be radial without necessarily being diametrically opposite each other.

It is not essential that the entire cuttingedge a 0 should be a straight line. It might also be a curve, provided it runs to the axis of the drill, and a practically sharp angle is procured there.

I claim as my invention- 1. Atwist drill having two grooves opposite each other, one groove being V-shaped and I In testimony whereof I have hereunto subhaving its apex in the axis of the drill. scribed my name.

2. Atwist drill havin one groove shaped so 7 as to form an angle with its apex in the axis OLUF T1 BERG 5 of the drill, While another is so shaped as to Witnesses:

leave a substantial connection between the I FRANK S. OBER, two sides of the drill. 1 EDWARD O. DAVIDSON. 

